A brake system is an apparatus that reduces speed and simultaneously stops a traveling vehicle and maintains a stopped state of the vehicle. The brake system includes a parking brake that reduces speed, stops a traveling vehicle, and maintains the stopped state of the vehicle.
A parking brake has a parking cable which is pulled by an operation of a lever provided at one side of a driver's seat inside a vehicle and maintains the vehicle in the stopped state by providing a braking force to a wheel linked to the parking cable. Conversely, when the lever is released, the parking cable is released and the braking force provided to the wheel is released.
In such a parking brake, since a driver has to operate the lever by a driver's intent, that is, whenever parking or traveling of the vehicle is initiated, use is very cumbersome. Accordingly, an electric parking brake (EPB) system in which a parking brake is automatically operated by a motor depending on a vehicle's operation state has been developed.
The EPB automatically operates or releases a parking brake and obtains safety in an urgent state in conjunction with a manual operation mode of a driver, a hydraulic electronic control unit (HECU), an engine electronic control unit (ECU), and a traction control unit (TCU) by a switching operation.
In such an EPB system, an ECU, a motor, a gear, a parking cable, a force sensor, and the like are integrally provided. Here, the ECU receives related information from the HECU, the engine ECU, the TCU, and the like through a controller area network (CAN), understands a driver's intent, and operates a parking brake actuator.
When the parking brake actuator is operated, a gear assembly is operated by driving of a motor, the parking cable is pulled by the operation of the gear assembly, a braking force is provided to a wheel, and accordingly the vehicle is maintained in a safe state. Here, the gear assembly may include a worm and a worm wheel which are connected to a rotational shaft of the motor to transmit a force.
Here, a high output is required to increase a braking force. A size of a motor which is applied is increased to increase the output. Conventionally, the worm and the motor are accommodated inside an actuator housing so that rotational shafts of the worm and the motor are parallel to each other. Since a position where the worm is accommodated has to be changed to change the size of the motor, there is a problem in that a separate housing has to be designed and provided for an increase in the size of the motor.